1. Field of the Invention
The present invention relates to tire sidewall compositions which exhibit improved ozone resistance and fatigue crack propagation resistance, as well as good sidewall adhesion to the tire carcass and good heat build-up.
2. Description of Information Disclosures
Rubber tires, such as pneumatic tires, include many components, such as, for example, sidewalls, which may be decorative and may have incorporated therein a titanium dioxide pigment. Sidewalls are continuously subjected to distortion under the normal road operating conditions, and the sidewalls are subjected to extensive continuous flexing and can crack under such flexing conditions. In addition to such flex cracking, such sidewalls are also subjected to atmospheric chemical action such as by ozone attack. The overall effect is that the sidewalls may erode and degrade and can even separate from the tire carcass during use and can cause the tire to fail.
Generally, the current practice in the manufacture of black sidewalls is to add chemical protectants to general purpose rubbers in an attempt to minimize ozone and flex cracking but they tend to be fugative and staining in the case of contact with white sidewalls combination. In some cases, and in particular white sidewalls, polymer blends have been used to effect improvement in ozone and flex resistance.
A composition which attempts to overcome these problems is disclosed in U.S. Pat. No. 3,508,595 to Wilson, and assigned to the General Tire & Rubber Company. This patent discloses a blend of chlorobutyl rubber, natural rubber, and ethylene propylene terpolymer as the protective cover for the white sidewalls used in such pneumatic tire construction.
U.S. Pat. No. 3,630,974 to Ladocsi, et al., assigned to Exxon Research and Engineering Company, further discloses the use of terpolymers for blending into high unsaturation rubbers in order to enhance their static ozone resistance. This patent also discloses a triblend of halobutyl rubber along with a terpolymer and a high-unsaturation rubber to improve dynamic ozone resistance and heat flex resistance. The terpolymers employed by this patentee comprise ethylene, propylene and a diene, and the high unsaturation rubber can include natural rubber, styrene butadiene rubber, and polybutadiene rubber, etc. It is again noted that various fillers can be used in these compositions, and among the variety of materials listed are various "oils" along with resins, waxes, etc. The patentee specifically discloses the use of 10 parts oil per 100 parts of rubber in these formulated blends. This patent also discloses that the terpolymer used will not include more than 10 or 20% of the diolefin therein. It is also noted that while U.S. Pat. No. 3,865,763 to Feniak, assigned to Polysar Limited, is primarily concerned with stabilization of halogenated butyl rubber with boron compounds, Example 5 of that patent discloses a combination of brominated butyl rubber with both an ethylene propylene rubber and a styrene butadiene rubber.
U.S. Pat. No. 3,830,274 to Waser, Jr., assigned to The Goodyear Tire and Rubber Company, discloses yet another elastomer blend for use in pneumatic tire sidewall compositions, which contains an ethylene propylene non-conjugated diene terpolymer along with bromobutyl rubber and a cis-1,4 polyisoprene rubber such as natural or synthetic rubber, along with a rubbery cis-1,4 polybutadiene with a specified molecular weight distribution. The patentee sates that this blend provides substantially improved hot flex-life and carcass adhesion properties for tire sidewalls.
U.S. Pat. No. 4,224,196 discloses a sidewall composition having improved flex resistance, wherein the blend composition comprises a blend of a halobutyl rubber, a highly unsaturated rubber and an oil extended EPDM terpolymer.
There is still a need for improvement in properties of tire sidewalls.